Apparatus for water removal from liquid-vapor contacting trays



Oct. 11, 1966 N. w. MITCHELL APPARATUS FOR WATER REMOVAL FROMLIQUID-VAPOR CONTACTING TRAYS Original Filed Aug. 10, 1961 FIG. 4

DOWNCOMER DOWNCOMER fl) 24 22 14 I TO TRAY BELOW FROM TRAY ABOVEINVENTOR N. w. MITCHELL. BY

FIG. 3

ATTORNEYS United States Patent O 3 Claims. (Cl. 261- 7) This is adivision of my copending application Serial No. 130,531, filed August10, 1961.

This invention relates to a liquid-gas contacting apparatus in which twoimmiscible liquids are present. In one aspect it relates to such anapparauts in which provision is made for separation and withdrawl of theheavier of two immiscible liquids during passage of gas or vapor in thedesired liquid-gas contacting operation.

In many instances liquid water is present in liquid-gas contactingcolumns in operations involving the contacting of non-aqueous liquidswith gases. Open steam is frequently used in stripping and fractionaldistillation columns. Such columns are sometimes operated under steamcondensing conditions and the condensate or water so formed flowsdownwardly in the columns displacing a portion of the desired internalreflux. When processing hydrocarbon liquids under such conditions wateris retained as the lower layer on each contacting tray. Retention timeof the hydrocarbon liquid undergoing contacting is reduced in proportionto the ratio of the volume of the hydrocarbon to the volume of thehydrocarbon plus water on a tray. For example, if the liquid on a trayis half water obviously the retention time and therefore the effectivecontacting time is reduced to one half of that in the absence of water.Also, water sometimes reduces the effectiveness of the liquidhydrocarbon-gas contacting just by its presence. For example, in theseething mass of liquid and gas on a vapor-liquid contacting tray it iseasy to visualize droplets of a liquid hydrocarbon surrounded by a filmof water thereby markedly reducing the desired effectiveness of thehydrocarbon-gas contacting.

An object of this invention is to provide vapor-liquid contactingapparatus for improving the efiiciency of vapor-liquid contactingoperations. Another object of this invention is to provide apparatuswhich is simple and relatively inexpensive to manufacture for improvingthe effectiveness of vapor-liquid contacting operations. Yet anotherobject of this invention is to provide apparatus for withdrawing anunwanted immiscible heavy liquid phase from vapor-liquid contactingtrays during normal operations. Other objects and advantages of thisinvention will be realized upon reading the following description whichtaken with the attached drawing forms a part of this specification.

In the drawing, FIGURE 1 is a sectional view of a portion of a.vapor-liquid contacting column provided with a water take-ofl trayassembly constructed in accordance with this invention. FIGURE 2 is ahorizontal sectional view of the vapor-liquid contacting column taken onthe line 2-2 of FIGURE 1. FIGURE 3 is a sectional view taken on the line33 of FIGURE 2. FIGURE 4 is a sectional view illustrating one embodimentof the drain trough of this invention and one means for water withdrawaltherefrom. FIGURE 5 illustrates another embodiment of the draw-offtrough. FIGURE 6 illustrates still another embodiment of the draw-offtrough. FIGURE 7 is an elevational view, partly in section, of alternatemeans for withdrawing water from one or more trays of a vapor-liquidcontacting column.

In the drawing, reference numeral 11 identifies a vaporliquid contactingcolumn such as a fractional distillation 3,278,169 Patented Oct. 11,1966 column provided with the apparatus of this invention. In thiscolumn a tray deck 12 is positioned horizontally and provided withvapor-liquid contacting bubble caps, valves or other suitable type ofvapor-liquid contacting apparatus 13. Reference numeral 14 identifies aplate extending below a column tray for defining a downcomer from onecontacting tray to the next. Plate 14a maintains a level of liquid ontray 12 in the downcomer area so that vapor will not pass upward throughthe downcomer. A plate 15 extends upward and is a weir plate while theplate 14 extends downward from weir plate 15 to define the downcomer toa next lower tray.

Between weir plate 15 and the main portion of tray deck 12 is a headertrough 17. This header trough is shown in FIGURES 1, 2, and 3. InFIGURES 1 and 3 is shown a plate 23 which is one wall of a trough 16illustrated specifically in FIGURES 2 and 3. At one end of header trough17 an opening 20 in the wall 11 of the vessel communicates with ahorizontal pipe 18 which is provided with a valve 19. Pipe 18 is soprovided that it can remove liquid from the bottom of the trough 17laterally and directed thru wall 11.

In FIGURES 1 and 2 is shown an alternative means for withdrawal ofliquid from the 'bottom of trough 17. This alternative means comprisesan opening 24, in weir plate 15. Opening 24 accommodates one end of apipe 21 which extends through the wall of the vessel as shown. Pipe 21is provided with a flow control valve 22. While either one of thesemeans for withdrawal of, for example, water, from trough 17 is operable,the embodiment involving opening 21 pipe 18 and valve 19 is preferred.

In the operation of the foregoing embodiment of the apparatus a vaporbeing processed passes upward in column 11 through the caps or valves 13to contact liquid flowing across the tray. Any water carried in thisliquid and particularly when the liquid is a hydrocarbon liquid tends tosettle to the surface of the tray or to seek a low point. I haveprovided a low level or low point for separation of the water. Thetroughs 16 are positioned at intervals across the tray and provide ampleopportunity for separation of water from the hydrocarbon liquid beingprocessed. Water collecting in troughs 16 flows into the header trough17 and ultimately through either opening 24 to pipe 21 or throughopening 20 to pipe 18 for disposal.

As illustrated in FIGURE 4, I provide an automatic means for removal ofwater from such a tray. This tray, however, is illustrated as being apunched or perforate tray 25 provided with troughs 26 which dischargeinto a header trough 27. Liquid from the bottom portion of header trough27 can pass through outlet pipe 28 for such disposal as desired. Such atray is provided with a weir plate 15 similar to that described inFIGURES 1 and 2. Since the level of liquid being treated is defined bythe height of the weir plate a liquid level controller, or interfacecontroller, 33 with its conventional auxiliary apparatus is provided. Asshown in FIGURE 4, this interface or level controller 33 is fed a signalfrom, for example, a float in response to its position as indicating aninterface between the water and the hydrocarbon oil and the controlleroperates a motor valve in response to this level of interface forwithdrawal of the heavy phase from the "header trough 27. Referencenumeral 29 identifies the wall of a vapor-liquid contacting columnprovided with the apparatus just described.

The particular vapor-liquid contacting apparatus illustrated, forexemplary purposes, in FIGURES 1 and 2 is intended to be the liquid-gascontacting apparatus described in US. Patent 2,979,316.

In FIGURE 3 of the drawing are shown the several troughs 16 in sectionwhich are shown in plan view in FIGURE 2.

As illustrated in FIGURES 1, 2, 3, and 4 the troughs have a square orrectangular cross section. It is not essential that the troughs 16 orthe header trough 17 be of such cross section because if desired, thecross section of these troughs can have other forms such as a V-shapedtrough 30 positioned below a tray deck 31 illustrated in FIGURE or thetrough can be a U- shaped trough 32 positioned below deck 33 asillustrated in FIGURE 6.

As mentioned hereinabove water is removed from vapor-liquid contactingcolumns for various reasons. In the operation of such apparatus asillustrated in FIG- URES l, 2, and 3 valves 19 and 22 can be operatedmanually if desired. If it is desired to make the water withdrawalautomatic the apparatus illustrated in FIG- URE 4 provides a simplesolution to the problem.

If desired, a single tray according to this invention can be provided ina vapor-liquid contacting column for water removal or if appreciablewater is to be withdrawn two or more trays can be provided with troughs16 and header trough 17 for Water removal. Such a column provided with aplurality of water draw-off trays is illustrated in FIGURE 7. In thisfigure a column 34 is provided with a plurality of water take-off trays46 as illustrated. Each of these trays is provided with suitablevapor-liquid contacting apparatus such as the apparatus described in theabove-mentioned patent or, if desired, conventional bubble capcontactors or other suitable type can be used. Each of these trays 46 isprovided with a header trough 35 and feeder trough 47. The water flowsfrom the tray deck into the feeder troughs and thence into the headertrough for removal from the column. Separate pipes 36 extend through thewall of the column for withdrawal of water from each header trough ofthe several trays. These pipes communicate with a header pipe 37arranged vertically along the outside of the column. At a level somewhatnear the ground level the header pipe 37 is provided with a small vessel38. Connected with vessel 38 is a vessel 41 provided with a float forsensing the position of the interface between the water 40 and a liquidhydrocarbon 39. The float in float vessel 41 transmits a signal to acontroller 43 which in turn transmits a signal to a motor valve 42 foropening or for throttling the valve depending upon the interface betweenliquids 39 and 40. When interface between these liquids is high themotor valve opens for withdrawal of water and when the interface reachesa predetermined level the motor valve closes. While this automatic waterwithdrawal means is in operation a valve 45 in a bypass pipe 44 isclosed. If, however, it is ever decided to operate this water withdrawalapparatus manually a valve 48 in the header conduit 37 is closed and themanually operable valve 45 is open. Since in many instances the amountsof water collecting on trays is not particularly large, such a valve asvalve 45 need be opened only at intervals during the columns operation.For example, it might be necessary only to open valve 45 once or twiceduring an eight hour shift. In such a case valve 45 is opened slightlyand maintained open as long as water discharges from the end of bypasspipe 44. When the first liquid in process appears, valve 45 is thenclosed.

Header pipe 37 as illustrated in the drawing is maintained full ofhydrocarbon liquid. Any water separated out on trays 46 and passingthrough troughs 45, header trough 35, and out from the column throughconnecting pipes 36 into the header pipe flows downward as a stream oras droplets of immiscible liquid in the liquid hydrocarbon in the headerpipe. This water being heavier than the liquid hydrocarbon flowsdownward and accumulates in the vessel 38. When water flows downwardthrough header pipe 37 the water-hydrocarbon interface in vessel 38rises. As mentioned hereinbefore when this interface rises to apredetermined level the float, liquid-level controller, motor valve 42operates to withdraw a portion of the water from vessel 38.

The top or upper end of the header pipe 37 can if desired be providedwith a vapor or fluid-tight cap or if desired the upper end of the pipecan be tied into the column.

Water entering header pipe 37 from an upper tray will not re-enter thecolumn on its downward descent in header pipe 37 because it falls freelytherein into the vessel 38.

In one instance and as an example of the specific apparatus of thisinvention, the depth or height of the troughs 16 and header trough 17was one and one-half inches while the distance from the top of thesetroughs or from the top surface of the vapor-liquid contacting tray tothe top of the weir plate was two and one-half inches. The diameters ofthese troughs 16 and the header trough 17 are sized such as toaccommodate amply the volume of water to be removed from the trays. Thatis, if large amounts of water are to be removed then these severaltroughs should have appreciable widths as for example, one to twoinches. In case only very minor volumes of water are to be removed,troughs 16 can be for example, one-fourth to one inch in width whileheader trough 17 is of a width of approximately two inches.

These troughs and other structural materials used therewith can, ifdesired, be the same materials as used in construction of the trays withwhich they are used.

While certain embodiments of the invention have been described forillustrative purposes, the invention obviously is not limited thereto.

I claim:

1. In an upright cylindrical fractional distillation column forseparating a first liquid phase from a second heavier liquid phaseimmiscible therewith, the combination of:

(l) a horizontal generally planar tray in the upper section of saidcolumn provided with means for effecting liquid-vapor contacting betweenvapor rising thru said column and liquid descending said column withphase separation on said tray;

(2) a header trough along and subjacent one edge of said tray forcollecting the heavier liquid, the radially outer wall of said troughextending to a level above the top of said tray;

(3) at least one trough in said tray for draining said heavier liquidinto the trough of (2);

(4) conduit means leading from the lower section of the trough of (2)thru the wall of said column substantially at tray level;

(5) a downcomer depending from said header trough;

and

(6) an upright weir on the upper surface of said tray extending acrosssaid column opposite said header trough.

2. Apparatus in combination comprising:

(1) an upright cylindrical fractional distillation column;

(2) at least one tray in an upper section of said column comprising:

(a) a generally horizontal flat plate engaging the wall of said columnalong the periphery of said plate except in a restricted section of saidcolumn in which the edge of said plate is substantially straight;

(b) a plurality of spaced-apart troughs depending from the plate of (a)and running generally perpendicular to its straight edge a substantialportion of the distance across said plate;

(c) a header trough along the straight edge of (a) communicating withthe troughs of (b), the outer edge thereof extending above plate level;

(d) openings in the plate of (a) intermediate said troughs and meanscovering said openings 5 6 for maintaining a liquid level on said trayand downcomer from the next tray above; an outlet conetfectinggas-liquid contact; and duit of (3) from each said tray; and means forcontrola depepding flange 011 the header trough of ling the flow ofliquid thru said outlet conduits.

(c) providing a downcomer to the next lower (3) tray;1 and d f h h d h f5 References Cited by the Examiner an out et con u1t rom t e ea er trougo c passing thru the wall of said column. UNITED STATES PATENTS 3. Theapparatus of claim 2 including a series of said 2,180,311 11/1939 King210-114 trays, alternate trays in said series being positioned cor- ,6 91953 M l y respondingly to the tray of (2), the trays intermediate 102,812,827 11/1957 Worly et a1. 210-114 X said alternate trays beingreversed so that the down- 2,917,372 12/1959 Wallin 261-114 comer of (e)extends to a line just above tray level and opposite the header troughof (c), the plate of (a) of REUBEN FRIEDMAN, Primary Examiner. each traybelow the uppermost being provided with an upright weir on its uppersurface radially inside of the 15 SAMIH ZAHARNA Exammer

1. IN AN UPRIGHT CYLINDRICAL FRACTIONAL DISTILLATION COLUMN FORSEPARATING A FIRST LIQUID PHASE FROM A SECOND HEAVIER LIQUID PHASEIMMISCIBLE THEREWITH, THE COMBINATION OF: (1) A HORIZONTAL GENERALLYPLANAR TRAY IN THE UPPER SECTION OF SAID COLUMN PROVIDED WITH MEANS FOREFFECTING LIQUID-VAPOR CONTACTING BETWEEN VAPOR RISING THRU SAID COLUMNAND LIQUID DESCENDING SAID COLUMN WITH PHASE SEPARATION ON SAID TRAY;(2) A HEADER TROUGH ALONG AND SUBJACENT ONE EDGE OF SAID TRAY FORCOLLECTING THE HEAVIER LIQUID, THE RADIALLY OUTER WALL OF SAID TROUGHEXTENDING TO A LEVEL ABOVE THE TOP OF SAID TRAY; (3) AT LEAST ONE TROUGHIN SAID TRAY FOR DRAINING SAID HEAVIER LIQUID INTO THE TROUGH OF (2);(4) CONDUIT MEANS LEADING FROM THE LOWER SECTION OF THE TROUGH OF (2)THRU THE WALL OF SAID COLUMN SUBSTANTIALLY AT TRAY LEVEL; (5) ADOWNCOMER DEPENDING FROM SAID HEADER TROUGH; AND (6) AN UPRIGHT WEIR ONTHE UPPER SURFACE OF SAID TRAY EXTENDING ACROSS SAID COLUMN OPPOSITESAID HEADER TROUGH.